In FIG. 5, there is shown a conventional turn signal canceling mechanism. As shown in the drawing, the turn signal canceling mechanism 10 includes: a canceling cam 11 turned integrally with a steering shaft; a turn bracket 14 attached to a case 13 so that the turn bracket 14 can be turned from a neutral position to a right or a left turning position being linked with a turn signal lever 12; a back plate 16 having a pair of arms 15 which are arranged on the right and left; and a ratchet 17 attached to the case 13 so that the ratchet 17 can be advanced and retracted.
Moderation pieces 18 and moderation springs 19 are respectively incorporated into the right and the left end portions of the turn bracket 14. These moderation pieces 18 come into pressure contact with moderation ridges 20 arranged in the case 13. Therefore, the turn bracket 14 can be held at the neutral position, the right turning position or the left turning position by these moderation pieces 18 and the moderation springs 19. On an upper face of the turn bracket 14, there are provided a pair of protrusions 21 which are arranged on the right and left, and the back plate 16 is 1 attached to both protrusions 21 in such a manner that the back plate 16 can be linearly reciprocated. The back plate 16 is held at a neutral position by the back spring 22 arranged between both protrusions 21.
The ratchet 17 has a protrusion 23 formed on the upper face, a protrusion 24 formed on the lower face, and a step portion 25. The upper protrusion 23 is engaged with a long groove 26 formed on an upper cover of the case, and the lower protrusion 24 slidably comes into contact with a cam face 27, the profile of which is an angle-shape, arranged inside of the forward end of the turn bracket 14. There is provided a ratchet spring 28 in the step portion 25 on the lower face. This ratchet spring 28 biases the ratchet 17 toward the canceling cam 11.
The structure of the conventional turn signal canceling mechanism 10 is described above. As shown in FIG. 5, when the turn bracket 14 is located at the neutral position, the lower protrusion 24 slidably comes into contact with a top portion of the ridge of the cam face 27, and a forward end portion of the ratchet 17 retracts from a rotational locus of the canceling cam 11.
When the turn lever 12 is operated, the turn bracket 14 is turned to the right turning position or the left turning position and held at the position by the actions of the moderation ridge 20, moderation piece 18 and moderation spring 19. When the turn bracket 14 is turned, the lower protrusion 24, which slidably comes into contact with the top of the ridge of the cam face 27, slidably comes into contact with a bottom portion. Therefore, the ratchet 17 advances along the long groove 26, and the forward end portion proceeds into the rotational locus of the canceling cam 11, and a base end portion of the ratchet 17 comes close to one of the arms 15.
When the turn bracket 14 is located at the right or the left turning position and also when the canceling cam 11 is turned in the same direction as that of the steering shaft according to the turn of the steering shaft, the canceling cam 11 is engaged with a forward end of the ratchet 17, and the base end portion of the ratchet 17 is turned in a direction so that it can be separate from the arm 15 which has been located close to the base end portion of the ratchet 17. On the other hand, when the canceling cam 11 is turned in the opposite direction, the base end portion of the ratchet 17 is engaged with the arm 15 which is located close to it. Therefore, the turn bracket 14 is returned to the neutral position integrally with the back plate 16.
When the turn signal lever 12 is turned by an operator's hand and held at the position as it is, the turn bracket 14 integrated with the lever 12 is locked at the right turning position or the left turning position. When the canceling cam 11 is turned in the opposite direction under the condition that the turn bracket 14 is locked at the right turning position or the left turning position, the base end portion of the ratchet 17 is engaged with the arm 15 which is located close to it, and a torque of the canceling cam 11 is transmitted to the back plate 16. Therefore, the back spring 22 is compressed, and the back plate 16 is moved to the right or the left along the protrusion 21, so that a disengagement of the ratchet 17 is caused.
In this connection, in the above conventional turn signal canceling mechanism 10, it is necessary to provide three types of springs including the moderation spring 19, the back spring 22 and the ratchet spring 28. As a result, the number of parts is large, and the production cost is raised.
The present invention has been accomplished to solve the above problems. It is an object of the present invention to provide a turn signal canceling mechanism capable of lowering the cost by reducing the number of spring types.